Trends in myocarditis incidence, complications and mortality in Sweden from 2000 to 2014

Investigate trends in myocarditis incidence and prognosis in Sweden during 2000-2014. Little data exist concerning population-trends in incidence of hospitalizations for myocarditis and subsequent prognosis. Linking Swedish National Patient and Cause of Death Registers, we identified individuals ≥ 16 years with first-time diagnosis of myocarditis during 2000-2014. Reference population, matched for age and birth year (n = 16,622) was selected from Swedish Total Population Register. Among the 8 679 cases (75% men, 64% < 50 years), incidence rate/100,000 inhabitants rose from 6.3 to 8.6 per 100,000, mostly in men and those < 50 years. Incident heart failure/dilated cardiomyopathy occurred in 6.2% within 1 year after index hospitalization and in 10.2% during 2000-2014, predominantly in those ≥ 50 years (12.1% within 1 year, 20.8% during 2000-2014). In all 8.1% died within 1 year, 0.9% (< 50 years) and 20.8% (≥ 50 years). Hazard ratios (adjusted for age, sex) for 1-year mortality comparing cases and controls were 4.00 (95% confidence interval 1.37-11.70), 4.48 (2.57-7.82), 4.57 (3.31-6.31) and 3.93 (3.39-4.57) for individuals aged < 30, 30 to < 50, 50 to < 70, and ≥ 70 years, respectively. The incidence of myocarditis during 2000-2014 increased, predominantly in men < 50 years. One-year mortality was low, but fourfold higher compared with reference population.